Liquid crystal display (LCD) devices have become the most important type of flat panel display devices at present. The display of a liquid crystal display device is based on pixels (or sub-pixels). A pixel electrode and a common electrode are included in each pixel, and an electric field can be generated between these two electrodes to drive liquid crystals corresponding to the pixel to be twisted. Thus, the amount of light transmitted through the pixel is changed, so that required content is displayed on the liquid crystal display device as a whole.
Advanced super dimension switch (ADS) mode liquid crystal display devices belong to a kind of liquid crystal display device, in which, a multi-dimensional electric field is formed by an electric field produced at edges of slit electrodes on a same plane and an electric field produced between the layer of the slit electrodes and the layer of a plate-like electrode, so as to allow liquid crystal molecules at all orientation within a liquid crystal cell, which are located directly above the electrode and between the slit electrodes, to be rotated, and thereby work efficiency of liquid crystals can be enhanced and transmissive efficiency is increased. The advanced super dimension switch technology can improve the picture quality of TFT-LCD (Thin Film Transistor-Liquid Crystal Display) products, and has advantages such as high resolution, high transmittance, low power consumption, wide viewing angles, high aperture ratio, low chromatic aberration, push Mura-free, etc.
FIG. 1 is a top view showing one pixel unit of an array substrate of an existing ADS mode liquid crystal display device. FIG. 2 is a schematic view showing a cross-section of the one pixel unit of the array substrate of the existing ADS mode liquid crystal display device taken along line A-A′.
As shown in FIG. 2, a common electrode 2 in the shape of a plate is located on an array substrate 9, the common electrode 2 is covered by an insulating layer 7 (for example a silicon dioxide layer), and on the insulating layer 7 there is provided a pixel electrode 1. The pixel electrode 1 includes a plurality of pixel electrode strips 11 which are spaced at an interval. When voltage difference is applied across the pixel electrode 1 and the common electrode 2, a multi-dimensional electric field that can acts to drive liquid crystals to rotate can be generated between the pixel electrode strips 11 and the common electrode 2.
As shown in FIG. 1, in order to reduce color deviation, the pixel electrode strips 11 of the pixel electrode 1 in one pixel unit which has the profile of one rectangle can be divided into two groups as a whole, which groups are respectively located in the upper part and in the lower part as shown in FIG. 1. The pixel electrode strips 11 in each group are parallel to each other, while the extension lines of the two groups of the pixel electrode strips 11 cross each other at a certain angle, which design is also referred to as “a tapered electrode”. Certainly, in a complete pixel unit, a thin film transistor and other structures should also be included, and they will not be described here for the purpose of simplicity.
In the ADS mode liquid crystal display device, because the common electrode 2 and the pixel electrode 1 are apart from each other at a short distance and have a large opposing area therebetween, the pixel unit has overlarge storage capacitance (Cst). Storage capacitance is a feature necessary for performing liquid crystal display, and is useful for maintaining the electric field in the pixel unit when a voltage is not applied to the pixel electrode, so that display pictures can become stable. However, if storage capacitance is overlarge, then on one hand, it will lead to slow charging of a storage capacitor, thereby resulting in a display error along the line of A gate line (H-block, horizontal block), and on the other hand, it will lead to slow discharging of the storage capacitor, and afterimage phenomenon occurs (Line-IS, line afterimage). When the display device has a relatively high refresh frequency, these issues become more serious. Generally, as to some certain picture for detection, overlarge storage capacitance is manifested with pictures of being greenish.
The pixel units of the existing advanced super dimension switch mode liquid crystal display devices suffer from such problems that the storage capacitance is overlarge or unstable, and the requirement on production precision is high.